1. Double Pipe HEAT EXCHANGERS with Finned Inner Tube
P M V Subbarao
Professor
Mechanical Engineering Department
I I T Delhi
Ideas for Creation of Compact HX!!!

2. How to decide the height of fin for a Double Pipe HX ?

3. nth order Longitudinal Fins
x=a=0 b
x=b x qb L b qb
x=b
x=a=0 x

4. Accounting of Heat Transfer due to Fins
h, should be resulting heat transfer coefficient on annulus side.
Fins with surface area, Afin, communicate as much as heat as an area of tube surface equal to hfinAfin .
Therefore, the total annulus side effective area is Atube + hfinAfin.
The ratio of total surface area to effective surface area is called as overall finned tube efficiency factor.

5. Performance of Least Material Fin
Strip fin
Triangular fin
Parabolic fin

6. Effective annulus side overall heat transfer coefficient:
Overall Heat Transfer coefficient of finned Double tube HX:

7. Performance of Least Material Strip Fin
Optimum shape for a given qb & qb
And solve for Ap with [ tanh (1.4192) = ]

10. Triangular Fin : Adiabatic Tip
The particular solution for
is:
The fin heat dissipation is:
The fin efficiency is:

11. Triangular Fin : Adiabatic Tip

12. Optimum Shape (Minimum Material) for Triangular Fin

14. Longitudinal Fin Of Concave Parabolic Profile
The differential equation for temperature excess is an Euler equation: L b qb
x=b
x=a=0 x

15. Optimum Shapes (Least Material) of Parabolic Profileqb
x=b
x=a=0 x
The heat dissipated is:
And the efficiency is:

16. Double Pipe HX with finned inner Tube
Equivalent diameter of annulus heat transfer, De:

17. Longitudinally Welded strip fins

18. Accounting of Heat Transfer due to strip Fins
h, should be resulting heat transfer coefficient on annulus side.
Fins with surface area, Afin, communicate as much as heat as an area of tube surface equal to hfinAfin .
Therefore, the total annulus side effective area is Atube + hfinAfin.
The ratio of total surface area to effective surface area is called as overall finned tube efficiency factor.

19. Effective annulus side overall heat transfer coefficient:
Overall Heat Transfer coefficient of finned Double tube HX: